Patients with a histologically aggressive disease (Hürthle cell, poorly differentiated, widely invasive follicular carcinoma or with an aggressive variant of papillary thyroid cancer, including tumors harboring a BRAF V600E mutation) may demonstrate less differentiated cancer cells, with low serum Tg and no 131I uptake. The gene discussed is BRAF; the disease is thyroid gland papillary carcinoma.